The use of magnesium or magnesium-containing compounds to catalyze the conversion of hydroxy aldehydes to dihydroxy esters by the so-called Tishchenko reaction is known. Thus, magnesium ethyl iodide has been used to catalyze this reaction, as described by Franke and Kohn in Monatsheft Fur Chemie, vol. 25, page 865 (1904).
More recently, U.S. Pat. No. 3,852,335 (Merger et al) discloses the conversion of hydroxypivaldehyde using hydroxides, oxides, and hydrated oxides of various metals, such as magnesium, in anhydrous medium or with addition of water. U.S. Pat. No. 3,862,215 (Merger et al) discloses the use of solid magnesium hydroxide and magnesium oxide for the conversion of hydroxy aldehydes to dihydroxy esters, the catalysts being "advantageously used in finely divided form". Even more recently, U.S. Pat. No. 5,041,621 (Morris and Luce) discloses the production of dihydroxy esters from specified hydroxy aldehydes utilizing a catalytically active elemental metal selected from magnesium, zinc, manganese, aluminum, titanium, or calcium. According to the last-mentioned patent, only small amounts of the metal (preferably magnesium) are required, and the metal is introduced into the reaction zone as a powder.
The addition to and use of solid catalyst materials, such as metal or metal oxide powders, in the hydroxy aldehyde reaction liquid, suffer from a number of disadvantages. For example, powders present difficulties in handling, are not easily metered into the reaction zone, and are often removed from the product mixture only with difficulty. In addition, they may deposit in quiescent areas of the reaction zone, and, unless eventually partially or fully dissolved in the reaction liquid, require effort to maintain adequate distribution thereof in the liquid. In short, a catalyst and procedure for the production of dihydroxy esters that avoided or minimized the difficulties associated with solid catalysts might have great economic value. The invention is such a catalyst and procedure.